A door opening and closing apparatus disclosed in Patent document 1, for example, is known. The aforementioned door opening and closing apparatus includes a step member fixed to a body of a vehicle and made of resin. A lower rail extending in a front-rear direction of the vehicle is provided at the step member. In addition, plural pulleys are supported at the step member in a manner that the pulleys are arranged adjacent to the lower rail in a width direction of the vehicle. A belt is engaged at the plural pulleys. The door opening and closing apparatus also includes a guide roller unit fixed to a slide door. The guide roller unit is fixed to the belt so as to integrally move with the belt and is mounted to the lower rail so as to move in the front-rear direction of the vehicle along the lower rail. The belt is driven by a drive member so as to open and close the slide door.